Quarterly Tax Estimator

If you earn money the IRS doesn't already tax through payroll, freelancing, running an LLC, consulting, contract work, the government still wants its share four times a year, not once in April. That is what quarterly estimated taxes are: prepayments toward the income tax and self-employment tax you'll owe when you file. Miss them, underpay them, or pay them late, and the IRS adds an underpayment penalty on top of the tax. The estimator above gives you a realistic per-quarter number in seconds. This guide explains what's behind it and how to stay penalty-free.

Who has to pay quarterly estimated taxes

As a rule, you owe quarterly estimates if you expect to owe at least $1,000 in federal tax for the year after subtracting any withholding. That sweeps in most self-employed people, freelancers, single-member LLC owners, partners, S-corp shareholders taking distributions, landlords, and anyone with significant investment or side income. If all your income runs through a W-2 job where tax is withheld from each paycheck, you usually don't need to file estimates, your employer is effectively paying them for you.

The grey area is people with a mix: a salaried job plus a growing side business. Withholding from the day job may cover part of your bill, but the side income is untaxed until you account for it. That is exactly why the estimator asks for your withholding separately, so it only charges you for the gap.

How the quarterly amount is actually calculated

Your annual federal tax has two layers when you're self-employed, and the calculator handles both:

• Self-employment tax. This funds Social Security and Medicare, the equivalent of the payroll taxes an employer and employee split. It runs 15.3% on roughly 92.35% of your net business profit. Half of it is deductible against your income tax, which the tool accounts for.
• Federal income tax. This is applied to your taxable income after the standard deduction, using the progressive brackets. Each slice of income is taxed at its own rate, so a higher bracket never penalizes your earlier dollars.

Add those two, subtract anything already withheld, and divide by four. That's your estimated quarterly payment. Clean books make this painless, which is why ongoing QuickBooks bookkeeping or Xero accounting pays for itself: you always know your profit, so the estimate is accurate instead of a guess.

The 2026 quarterly deadlines

Estimated payments follow four windows, each covering a slice of the year. For the 2026 tax year the due dates fall around April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027. Note the periods are uneven, the second "quarter" is only two months, so don't assume an even calendar split. If a date lands on a weekend or holiday it shifts to the next business day.

How the underpayment penalty works, and how to avoid it

If you don't pay enough through the year, the IRS charges an underpayment penalty calculated like interest on the shortfall, accruing from each missed deadline. The good news is there are clear "safe harbors" that switch the penalty off entirely:

• Pay at least 90% of the current year's tax through estimates and withholding, or
• Pay 100% of last year's tax (110% if your prior-year adjusted gross income was over $150,000).

The prior-year safe harbor is the simplest shield: if you simply pay what you owed last year, spread across the four quarters, you cannot be penalized this year no matter how much your income grows. That's the strategy many founders use in a high-growth year.

Common mistakes that trigger penalties

The errors we fix most often are predictable. People forget that the four windows are uneven and short-pay the June deadline. They calculate income tax but forget self-employment tax, which is often the larger piece for a profitable solo business. They spend the money earmarked for taxes and scramble at year end. And foreign-owned LLC owners sometimes assume "no US tax due" means "nothing to pay," overlooking that Form 5472 obligations and effectively-connected income can still create liability.

One more: treating the estimate as exact. It isn't. The number above is a strong planning figure, but credits (child tax credit, education credits), itemized deductions, retirement contributions, and state income tax all move the final result. Use the estimate to fund a tax savings account; use a professional to lock in the precise filing.

A simple system that works

The cleanest approach is to open a separate savings account, and every time you get paid, move a fixed percentage into it, often 25–30% of profit for a moderate earner. When each quarterly deadline arrives, you pay from that account and never feel it. Pair that habit with bookkeeping that closes monthly, and quarterly taxes stop being a fire drill. If you'd rather not run the math at all, our team prepares estimates as part of US tax filing and keeps you on schedule all year.

When to bring in a CPA or EA

Run the estimator any time your income changes, a big new client, a slow quarter, a one-off windfall, and adjust the next payment up or down. But if your situation has real complexity, multiple states, an S-corp election, foreign income, large equity events, the safe-harbor math and multi-state estimates are worth handing to a professional. A licensed CPA or Enrolled Agent can set your quarterly schedule, file the vouchers, and represent you if a notice ever arrives. That's the difference between a rough estimate and a number you can rely on.

How to adjust mid-year when income changes

One advantage of quarterly estimates is that they're not locked in January. Each payment is a fresh chance to recalibrate. If you land a big new client in the spring, bump the next payment up so you don't fall behind. If a quarter is slow, you can ease off, as long as you still meet a safe harbor by year end. Re-running the estimator whenever your outlook shifts keeps you from either overpaying (an interest-free loan to the IRS) or underpaying (a penalty). Founders with lumpy, project-based income benefit most from this: rather than guessing a flat annual figure, they true up each quarter against what actually happened.

It also pays to coordinate estimates with retirement contributions. Money you put into a SEP-IRA or solo 401(k) reduces taxable income, which lowers your estimated tax. If you plan a large contribution, factor it in before you size your payments, otherwise you'll over-fund the IRS and wait until filing to get it back.